Patent documents 1, 2 and 3 disclose processes for production of methyl methacrylate by reaction of methylacetylene with carbon monoxide and methanol, using palladium compounds, proton acids and phosphine compounds as catalysts. The methylacetylene used in such reactions is known to contain propadiene in a range of 0.2%-3%.    [Patent document 1] JP No. H02-277551 A    [Patent document 2] JP No. H09-501671 T    [Patent document 3] JP No. H02-290831 A